1. Field of the Invention
The present invention relates to a method of forming a nanostructure having a high aspect ratio and a method of forming a nanopattern by using the same; and more particularly, to a high-aspect ratio nanostructure forming method with simplified processing and excellent economical efficiency, and a nanopattern forming method using the same.
2. Description of the Related Art
The major trend in manufacturing of industrial parts since 1980s has been miniaturization, and this calls for the development of nano-sized structures, which will be referred to as nanostructures hereinafter. To meet the demand, there are many techniques introduced for easily and economically forming reliable nanostructures.
One of the representative methods for forming a nanostructure is nanoimprint lithography, which is disclosed in U.S. Pat. No. 5,772,905. To describe the technique in detail, a hard mold having a nano-sized pattern is formed by using electron beam lithography first and a substrate is coated with a polymer compound and heated to thereby have flexibility. Then, the hard mold is pressed under a strong pressure of about 1,900 psi to thereby form a nanostructure.
The nanoimprint lithography has an advantage that structures as small as tens of nanometers can be formed by using a mold of a high hardness. However, since the method requires a mold of a high hardness and high pressure, it is difficult to form patterns by using an engraved mold or molds having patterns of diverse sizes and to form a pattern in a wide area. Most of all, the nanoimprint lithography has a shortcoming that it is hard to form a structure having a high aspect ratio.
To resolve the problems, researchers have been developed diverse soft lithography techniques using relatively soft and elastic molds instead of using a hard mold. One of the soft lithography techniques is microcontact printing. According to the microcontact printing, a mold having a pattern is formed and the mold is coated with a chemical called poly-dimethylsiloxane (PDMS) on the embossments, and then the mold is pushed down on a substrate to thereby form a pattern. This method is similar to stamping a seal.
The microcontact printing has an advantage that it can form a desired pattern without leaving any remaining layer on the substrate. However, since the method should use a chemical material, i.e., PDMS, there is a shortcoming that it cannot form a structure having a high aspect ratio.
Another example of the soft lithography techniques is micromolding in capillaries (MIMIC), which is disclosed in U.S. Pat. No. 6,355,198. According to the MIMIC, a PDMS mold having a pattern is positioned in a substrate and a three-dimensional structure of a micrometer size is formed by flowing a fluid from the sidewall of the mold. When the MIMIC is repeated in several layers, a high three-dimensional structure can be formed. However, since multiple layers of molds should be arranged precisely to form a reliable structure having a high aspect ratio, the process is difficult and complicated.
Besides, there are other diverse soft lithography techniques. Most of them have an advantage that, since an elastic PDMS mold having a low hardness is used, a three-dimensional microstructure can be formed in a wide area, but they have a conclusive limitation that they can hardly form a nano-sized structure.
Meanwhile, another method of forming a nanostructure having a high aspect ratio is atomic force microscope lithography. The atomic force microscope lithography forms a nanostructure having a high aspect ratio by operating a probe of an atomic force microscope and contacting the probe with polymer physically. Although the method has an advantage that delicate structure can be formed, it has a shortcoming that the process is remarkably slow because every single structure should be formed with the probe and, accordingly, it can be hardly applied to a wide area.
Other nanostructure forming methods include Micro Electro Mechanical system (MEMS) processing, Deep Reactive Ion Etching System (DRIE), and conventional light exposure processing such as electron beam lithography and photolithography. Most of the methods have been used for the fabrication of semiconductors conventionally. Although there are more or less differences, they require a light exposure process in common. Therefore, they have shortcomings that they should use multiple sheets of masks, that the process is complicated and takes long time, and that they require a high amount of costs.